In the sorting of articles, such as beans, one method of detecting defective products has been to reflect light from the individual beans and detect the reflected light at two different light wavelengths. Defective beans are usually discolored and differ from normal beans in that they produce a different ratio of reflected light at the two selected wavelengths.
In all such apparatus for sorting articles one important factor is the need to pass each article, such as beans, past the inspection point substantially in single file order. One such satisfactory means is disclosed in the copending application, Ser. No. 687,981, filed May 19, 1976, entitled A FEED WHEEL FOR A SORTING APPARATUS. In this apparatus articles are fed from a central hopper by the use of a revolving wheel assembly which picks the articles from the supply and propels them individually through an optical scanner. Such an optical scanner is described in copending application, Ser. No. 687,950, filed May 19, 1976, entitled LIGHT AND COLOR DETECTING SCANNER FOR SORTING APPARATUS. This detecting scanner comprises the combination of a sealed enclosure penetrated by a transparent sleeve through which the articles to be sorted are propelled individually, illuminating means providing a thin homogenous plane of light extending substantially perpendicular to the path of the articles, a first set of optically filtered photodiodes connected in parallel which are responsive to light of a chosen wavelength and which are arranged uniformly about the glass sleeve both above and below the plane of illumination so as to uniformly detect light reflected from all surfaces of the articles being sorted as they individually pass through the plane of illumination, a second set of optically filtered photodiodes connected in parallel which are responsive to light of a second wavelength and which are uniformly and symmetrically interspersed with the first set of photodiodes so as to also uniformly receive light reflected from all surfaces of the articles being sorted, means to adjust the sensitivity of each set of photodiodes to predetermined levels, means to connect the illuminating means to an externally regulated power supply, and means to connect the outputs of the two sets of photodiodes to a control apparatus.
Previous apparatus for color-sorting applications have suffered greatly because of the great amount of operator skill and technical sophistication required to make the operation profitable. Typical of the steps required to set up previous apparatus are such itmes as determining which color background standard to use with an appropriate filter selection, both selections depending on the hues of colors encountered in the product to be sorted. Once selected these must be installed in the optical head taking care to see that they are clean.
Since the selection of filters is usually a trial and error process this can prove to be a lengthy procedure. Slits must be chosen (if used) based on the size of the product to be sorted. The electronic control system can now be set up after warmup (usually 1/2 hour if phototubes are used) after which time the phototubes can be standardized, the background selected, evaluated and if acceptable, the system can be adjusted for optimum sorting. Reject selectors, air pressures, delay time for rejectors, duration of reject time and then final adjustments or fine tuning must now be made for optimum sorting accuracy.
Since milling-warehouses and other dry produce sorting establishments where sorting apparatus are used to not generally have access to a labor force with the high degree of technical skill required to have an in-depth understanding of the machine and its adjustments, and since further the interaction between adjustments are such that a person having considerable training with the machine is required, it can be seen that these establishments, which are usually low profit margin operations as well as being seasonal, need apparatus which can be operated by relatively unskilled persons. Further compounding the problem is the requirement that the apparatus usually has to be trimmed on a continuing routine basis after the initial setup to correct for drift stemming from dust buildup and temperature related gain variations. Also, in prior apparatus it is not readily apparent to the operator whether the apparatus is continuing to reject at the levels originally set without diverting the sorted product from the main collection hopper and examining it on a statistical basis. The apparatus is usually stopped during the examination to prevent contamination of the already sorted product, further causing a loss of productive time. As a result of the aforementioned problems, such apparatus often runs at less than top efficiency or sits idle for long periods awaiting repair or adjustment by a technician or a manufacturer's representative.
In several prior art systems a log-anti-log analog divider or pulse width modulating scheme has been used to give the quotient of the ratio of two signal channels. Where a signal is required that is proportional to the ratio, for example, for proportional control of a system, such schemes are necessary. However, if this quotient is compared to a constant to render threshold information, the analog division is unnecessary.
The following description will show how the analog division circuitry of the prior art is circumvented, thus allowing a relatively simple, drift-free electronic control package. It further will be shown how these problems have been circumvented, and that when the invention is used in combination with the invention of the previously identified copending application entitled: LIGHT AND COLOR DETECTING SCANNER FOR SORTING APPARATUS, a highly accurate and stable sorting apparatus is provided. In operation, the only critical adjustments made by the operator are the reject thresholds and adjusting of these thresholds has been simplified by displaying the reject rate information as feedback information to the operator.
It is, therefore, the primary object of this invention to provide an effective and economical control system, requiring minimum operator skill, to process the signals from a scanner such as that of the above-mentioned copending application. The output signal of the control system is a reject signal suitable for driving a solenoid-operated air blast rejection system.
Other features of the control system allow the reject threshold to be adjusted by the operator, that is the operator may adjust for the degree of discoloration that will cause the system to reject a product, such as a bean. There are two thresholds the operator may set, one threshold determines the rejection of beans that are darker than normal hue and the other threshold is for beans that are of a lighter than normal hue. Either or both may be enabled at the same time. In addition, the option of rejecting small foreign articles is provided and this threshold is factory adjusted.
Further included in the control system is a meter that displays the on-going rate of rejection for setting the dark and light thresholds, balancing the rejection rates of several processing channels in a multi-channel sorting apparatus, and indicating that the apparatus is functioning correctly.
Typically in the processing of articles a plurality of sorting devices are run in parallel in order to increase the processing rate. Although separately adjusted sorting devices can be used, such an approach requires further operator involvement, additional set up time and may result in different rejection criteria for each sorting unit. It is therefore desirable to provide a master unit having the various operator adjusted controls and a plurality of slave or tracker units that automatically follow the master sorting criteria. Also, by providing several units that are switchable between master and tracker operation, in the event of failure of a master unit, a tracker unit may be switched over to master operation in order to avoid down time of an entire system.